172 lines
2.9 KiB
HTML
172 lines
2.9 KiB
HTML
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>Note on Serial Flow Control</TITLE
|
|
><META
|
|
NAME="GENERATOR"
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.52"><LINK
|
|
REL="HOME"
|
|
TITLE="Linux PPP HOWTO"
|
|
HREF="index.html"><LINK
|
|
REL="UP"
|
|
TITLE="Configuring your modem and serial port"
|
|
HREF="modem.html"><LINK
|
|
REL="PREVIOUS"
|
|
TITLE="Configuring your modem"
|
|
HREF="x761.html"><LINK
|
|
REL="NEXT"
|
|
TITLE="Testing your modem for dial out"
|
|
HREF="x808.html"></HEAD
|
|
><BODY
|
|
CLASS="SECT1"
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#840084"
|
|
ALINK="#0000FF"
|
|
><DIV
|
|
CLASS="NAVHEADER"
|
|
><TABLE
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TH
|
|
COLSPAN="3"
|
|
ALIGN="center"
|
|
><A
|
|
HREF="http://www.linuxports.com/howto/ppp"
|
|
TARGET="_top"
|
|
>Linux PPP HOWTO</A
|
|
></TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="left"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="x761.html"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="80%"
|
|
ALIGN="center"
|
|
VALIGN="bottom"
|
|
>Chapter 12. Configuring your modem and serial port</TD
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="right"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="x808.html"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="SECT1"
|
|
><H1
|
|
CLASS="SECT1"
|
|
><A
|
|
NAME="AEN797"
|
|
>12.4. Note on Serial Flow Control</A
|
|
></H1
|
|
><P
|
|
>When data is traveling on serial communication lines, it can happen
|
|
that data arrives faster than a computer can handle it (the computer may
|
|
be busy doing something else - remember, Linux is a multi-user, multi-
|
|
tasking operating system). In order to ensure that data is not lost
|
|
(data does not over run in the input buffer and hence get lost), some
|
|
method of controlling the flow of data is necessary.</P
|
|
><P
|
|
>There are two ways of doing this on serial lines:-
|
|
|
|
<P
|
|
></P
|
|
><UL
|
|
><LI
|
|
><P
|
|
>Using hardware signals (Clear To Send/Request to Send - CTS/RTS).</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
>Using software signals (control S and control Q, also known as XON/XOFF).</P
|
|
></LI
|
|
></UL
|
|
> </P
|
|
><P
|
|
>Whilst the latter may be fine for a terminal (text) link, data on a
|
|
PPP link uses all 8 bits - and it is quite probable that somewhere in
|
|
the data there will be data bytes that translate as control S and
|
|
control Q. So, if a modem is set up to use software flow control, things
|
|
can rapidly go berserk!</P
|
|
><P
|
|
>For high speed links using PPP (which uses 8 bits of data) hardware flow
|
|
control is vital and it is for this reason that you must use hardware
|
|
flow control.</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="x761.html"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="index.html"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="x808.html"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>Configuring your modem</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="modem.html"
|
|
>Up</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>Testing your modem for dial out</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |